Predation by Coleps sp. (Ciliophora, Prostomatea) on polyps of Hydra (Cnidaria, Hydrozoa)

The present study reveals a novel predator-prey interaction in freshwater ecosystems: that of a free-living protozoan, Coleps sp., and polyps of the genus Hydra. Despite the common perception that larger body size confers competitive advantages, this finding shows that a large number of small-sized phagotrophic organisms, Coleps sp., attack Hydra polyps in groups, first attack their tentacles, and then gradually consuming the entire polyps. This finding was observed in Hydra vulgaris and Hydra sinensis specimens collected in freshwater bodies in São Paulo, Brazil. This discovery challenges traditional notions of size-based competitiveness and demonstrates that Coleps sp. can overcome the defensive barrier of hydra's cnidocytes. The study highlights the adaptability of Coleps sp. in its ability to prey not only on other protozoans, but also on multicellular organisms such as hydras. This suggests an even more complex predation dynamic that could have significant implications for the structure of freshwater zooplankton communities. This work provides a basis for future research into the ecological importance of “minor” predators such as Coleps sp. in regulating aquatic communities and underscores the need for more detailed studies to better understand the interactions between Hydra and Coleps sp., and how these relationships affect zooplankton populations and the overall dynamics of aquatic ecosystems.